package euler.p001_050;

import java.util.List;

import euler.MainEuler;

public class Euler021 extends MainEuler {

    /*
        Let d(n) be defined as the sum of proper divisors
        of n (numbers less than n which divide evenly into n).

        If d(a) = b and d(b) = a, where a ≠ b, then a and b
        are an amicable pair and each of a and b are called amicable numbers.

        For example, the proper divisors of 220 are
        1, 2, 4, 5, 10, 11, 20, 22, 44, 55 and 110; therefore d(220) = 284.

        The proper divisors of 284 are 1, 2, 4, 71 and 142; so d(284) = 220.

        Evaluate the sum of all the amicable numbers under 10000.
     */


    public String resolve() {

        int limite = 10000;
        int[] sumofproperdivisors = new int[limite];

        for (int i = 1; i < sumofproperdivisors.length; i++) {
            List<Integer> divisores = primeHelper.divisores(i);

            int suma = 0;
            for (Integer divisor: divisores) {
                suma+=divisor;
            }

            sumofproperdivisors[i]=suma-i;
        }

        int sumofalltheamicablenumbers = 0;
        for (int i = 1; i < sumofproperdivisors.length; i++) {
            if ((sumofproperdivisors[i] < sumofproperdivisors.length) &&
                    (sumofproperdivisors[i] != i) &&
                    (sumofproperdivisors[sumofproperdivisors[i]] == i)){
                sumofalltheamicablenumbers+=i;
            }
        }

        return String.valueOf(sumofalltheamicablenumbers);
    }

}
